An apparatus for uniform cooling of a single power electronics device, an array of discrete power electronics devices or types of other heat-generating by integrating discrete thermostatic expansion devices (TXVs) and their control directly into each discrete cold plate. The thermostatic expansion device is positioned such that a sensing element is located directly within the exit refrigerant stream.
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1. In a cold plate having an inlet to which a refrigerant that is sub-cooled is supplied and an outlet from which the refrigerant that is superheated exits the cold plate, between which inlet and outlet at least one passage for flowing the refrigerant internally through the cold plate is operatively arranged to cool at least one heat, generating device associated with the cold plate, the improvement comprising a thermal expansion valve and a sensing element operatively connected with the thermal expansion valve and arranged in the cold plate such the sensing element is located directly in a stream of the flowing refrigerant exiting the outlet of the cold plate so as to communicate a force created by a pressure change in the sensing element due to a temperature change in a refrigerant stream exiting the cold plate to alter a variable flow cross-sectional area of the thermal expansion valve.
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The present invention relates to a method and apparatus for ensuring adequate and uniform cooling for a single heat-generating device or an array of discrete heat-generating devices.
Heat fluxes and temperature uniformity constraints for modern electronics and optics are progressively demanding. As this occurs, the cooling technology for these components shifts from low-cost legacy solutions like air cooling and liquid cooling that produce heat transfer coefficients of 100 s to 1000 s of W/m2K to advanced thermal management solutions, such as vapor-compression cooling that can supply heat transfer coefficients up to 100,000 W/m2K.
Vapor compression technology has a limitation, however, when applying it to an arrayed heat load with many discrete sources. Supplying cooling to discrete sources (or circuits in an evaporator) has been historically accomplished via distributors located immediately downstream of the expansion device. These devices impose a high fluid velocity (which translates to a considerable pressure loss) through discrete orifices within the device. Each discrete orifice is dedicated to each discrete heat load. The momentum-driven separation will give near uniform flow distribution between the conduits at the cost of pressure loss. As the heat rejection temperature approaches the cooling temperature, the high-side pressure and low-side pressure of the system also converge, therefore making less pressure drop available to be used for flow balancing and further limiting the flow control of the pressure-drop balancing approach. Additionally, as the number of discrete cold plates (heat loads) increases; the size, weight, and complexity of the plumbing necessary to balance the two-phase flow-mixture downstream of the expansion device (and upstream of the cold plates) increases dramatically. Without the refrigerant flow uniformity to the individual cold plates, the temperature uniformity on and between cold plates will degrade rapidly, causing component failure in some cases.
We have discovered, however, an improved way to control the temperature uniformity of discrete heat loads using a vapor compression cooling scheme by integrating individual compact thermostatic expansion devices (TXVs) and their control directly into each individual cold plate. Individual control of each cold plate simplifies the overall system because the cold plates can all be maintained at a uniform temperature, regardless of the heat load to each individual cold plate, simply by maintaining a uniform outlet pressure of the superheated refrigerant exiting the cold plates, and ensuring that the cold plates are all supplied with sub-cooled liquid refrigerant at each cold plate inlet. By way of the present invention, the action of the integral TXV (of the cold plate) via opening or closing an internal orifice controls the flow to each cold plate. Thus, the control of each cold plate is localized, greatly reducing the overall control complexity. In addition, the inlet and outlet headers to the arrays of cold plates are simplified because the inlet headers have only subcooled liquid and outlet headers have only superheated vapor. This approach avoids individual two-phase distributor lines that must be balanced and fed to each cold plate.
In addition to saving space, plumbing complexity, and control complexity for the overall system, integrating the TXV within the cold plate also provides much faster TXV response time. Integrating the TXV into the cold plate also allows the sensing element to be integrated into the TXV. Integrating the sensing element with the TXV eliminates the capillary tube used in conventional TXV systems and improves the time response of the TXV because the sensing element can be immersed in the exiting refrigerant stream instead of relying on conduction of the outlet tube. Finally, with the integrated TXV configured as a cartridge, sealing can be accomplished via O-rings or other mechanical seals, thereby enabling field replacement of individual TXVs without the need of brazing or soldering, as is required for some conventional TXVs. Because of its enhanced temperature control, ability to be field replaceable, and augmented response time, the present invention enables the use of advanced power electronics, and more specifically, high-power lasers that demand temperature uniformity on the order of ±2° C. and full load “turn-on” times of less than 400 milliseconds.
As is well known in the art, the conventional TXV approach, as disclosed, in U.S. Pat. No. 4,750,334 whose FIG. 2 is repeated here as
U.S. Pat. No. 4,712,384 sought to integrate the TXV into the evaporator and thereby improve the conventional approach by integrating the sensing bulb and diaphragm into the outlet stream of the evaporator. However, that approach used an external mechanical “push rod” 82 to actuate the valve portion of the TXV, which was located in the inlet stream of the evaporator as seen in FIG. 4 and shown in the present application as
U.S. Pat. No. 5,297,728 discloses another attempt to eliminate the sensing bulb of the TXV and whose FIG. 1 is reproduced herein as
An object of the present invention is to provide a cartridge TXV that fundamentally differs in the method of temperature and refrigerant flow control that has been used in the past. First, the sensing element is integral to the TXV but is located external to and at the end of the TXV instead of within the TXV. Second, the integrated TXV is inserted into the evaporator outlet flow path. These two key differences eliminate two fluid connections and temperature variations experienced within the sensing bulb of U.S. Pat. No. 5,297,728. Third, having the sensing element immersed in the outlet stream of the evaporator and integral to the TXV enhances control because it eliminates the conduction resistance seen in conventional TXV arrangements.
An additional object of the present invention is to provide a method for improving and localizing the control of evaporative cold plates, while reducing the complexity of the remainder of the vapor compression system. The present invention goes beyond previous efforts to integrate TXVs into cold plates for vapor compression systems. U.S. Pat. No. 8,312,736 discloses an integrated TXV in a reverse-flow double pipe configuration. In this known configuration partially expanded refrigerant maintained above the ambient dew point flows through the outer pipe and then through an expansion device. Once through the expansion device, the cold refrigerant accepts heat from an electronics load and flows out through the inner pipe. This design seeks to eliminate condensation from sub dew-point cooling of electronics. The major drawback to this approach, however, is that the expansion is performed via fixed orifice (capillary tube) incapable of controlling the cooling temperature or the superheat into the compressor. Therefore, precise temperature control of sensitive electronics with varying ambient conditions and thermal loads cannot be performed with this device. Taking a different approach, the present invention integrates a cartridge TXV into a cold plate to provide active temperature control of sensitive electronics and eliminate the drawbacks of previous attempts.
These and further objects, features and advantages of the present invention will be seen by the following detailed description of a currently preferred, non-limiting embodiment of the present invention shown in the accompanying drawings wherein:
The conventional vapor compression cooling system has either a single external TXV that feeds a plurality of cold plates #1-3 via a distributor (shown in
In the present invention, the TXV is integrated directly into the cold plate and positioned so the outlet temperature sensing portion is located directly within the exit refrigerant stream, thereby improving the time-response of the valve, eliminating the need for heat ballasts and capillary tubes. More specifically,
Integrating a single TXV or multiple TXVs into the cold plate places the largest pressure drop of the system at the point of use. Thus, flow mal-distribution amongst multiple cold plates or multiple passages within a cold plate is eliminated by way of the present invention. Additionally, local refrigerant flow metering results in a high degree of thermal control for massively arrayed and distributed systems. Finally, the inlet and outlet plumbing to the cold plate are both single phase. Thus, gravitational effects related to flow separation or density dependent flow variations from curved plumbing or flow splitting are all eliminated from the inlet and outlet ports and associated manifolds.
In some applications, including high-heat-flux electronics cooling, where the heat load must be cooled with low-vapor-quality refrigerant (to establish the desired heat transfer regime) and the temperature must remain uniform across a large surface area, the cold plate exit quality could be less than 1.0 (meaning the exit flow is a two phase mixture and not a superheated vapor). If this is the case, a recuperative heat exchanger can be used to completely vaporize the fluid exiting the cold plate before it reaches the integrated TXV sensing bulb. In addition to providing the superheat necessary to control the activation of the TXV, this approach also serves to protect the vapor compression system by preventing liquid refrigerant (in the two phase mixture) from returning to the compressor, which can cause damage to bearings, valves, and connecting rods. Also, it ensures that only liquid refrigerant enters the TXV, thereby stabilizing the flow across the valve.
Functionally, this second embodiment with the integral recuperative heat exchanger shown in
The TXV cartridge is designed to be inserted directly into a blind hole in the cold plate and sealed with three conventional O-rings. As shown in
As shown in
Although the integrated TXV cartridge of the present invention operates in a manner somewhat similar to a conventional TXV because it actuates the valve based on superheat-induced pressure, there are four fundamental and significant differences between the two, namely:
In summary, a cold plate with an integrated TXV according to the present invention provides faster time response, provides more precise thermal control, eliminates distributor problems in large arrayed systems, allows for field replacement of the TXV without brazing, and provides a more compact and higher performance solution in comparison to conventional systems.
While the currently preferred embodiments of the invention have been illustrated and described, it should be understood that, after reading this disclosure, variations to this embodiment will be apparent to one skilled in the art without departing from the principles of the invention described herein. Therefore, we do not intend to be limited to the details shown and described herein but intend to cover all such changes and modifications as are fairly encompassed by the scope of the appended claims.
Sykes, David M., Dominico, Joshua C., Scaringe, Robert P., Cole, Gregory S., Staples, Daniel A.
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